This disclosure relates to semiconductor integrated circuit (IC) fabrication generally, and more specifically to multipatterning techniques. In semiconductor fabrication processes, the resolution of a photoresist pattern begins to blur at about 45 nanometer (nm) half pitch due to diffraction. To continue to use fabrication equipment purchased for larger technology nodes, multi-exposure methods have been developed.
Multiple exposure or multi-patterning technology (MPT) involves forming patterns on a single layer of a substrate using two or more different masks in succession. If only two masks are used for patterning a layer, the technique is referred to as double exposure. One form of double exposure is referred to as double patterning technology (DPT). In DPT, first and second masks are used sequentially to pattern the same layer. As long as the patterns within each mask comply with the relevant minimum separation distances for the technology node, the combination of patterns formed using both masks may include smaller separations than the minimum separation distance. MPT allows line segments, and in some cases, more complex shapes to be formed of a vertical segment and a horizontal segment on the same mask. Thus, MPT provides flexibility and generally allows for significant reduction in overall IC layout. If two or more masks are to be used, it is customary to refer to the patterns as being assigned one of two “color types”, where the color corresponds to a mask assignment.